The broad objective is a better understanding of embryonic development in terms of its genetics and of the biochemical compounds and interactions which control it. In this proposal, specific attention is focused on several properties of the complex t-mutants and on the modulation of alpha-fetoprotein synthesis in embryonic visceral endoderm cells. New mutants which interact with T to give tailless mice, but lack the other properties of t-haplotypes obtained from the wild mouse population, will be isolated after nitrosourea mutagenesis of males. The mutants will be used to determine the relationship between the mutant locus and the genes Tp63 and T. The enhanced transmission of t-bearing sperm observed with tw5 males under normal breeding conditions will be studied by in vitro fertilization. The conditions or treatments which permit segregation distortion in vitro should suggest the biochemical or physiological basis for the difference between t and wild-type sperm and permit identification of the compounds or components involved. The goal is to learn how mutation in the t-region alters sperm of only one type and which t-region genes are involved. Synthesis of alpha-fetoprotein is inhibited in 8th day visceral endoderm by contact with the underlying extraembryonic ectoderm. The mechanism by which the synthesis of this oncofetal protein is modulated will be studied using cell lines prepared from 8th day visceral endoderm and extraembryonic ectoderm. The lines are obtained by hybridizing embryonal carcinoma cells with the appropriate embryonic cells or by SV40 transformation. The goal is to determine the level at which regulation occurs and then to obtain the modulation of alpha-fetoprotein synthesis in endoderm cells using cell-free material derived from the extraembryonic ectoderm line. The components responsible for the modulation can then be isolated.